How do I import upstream commits into ELPA

Hi all,
A few months ago Stefan pushed a small fix to my compact-docstrings package. I
wanted to upstream it to the GitHub repository today, so I ran the following:
git remote add github-compact-docstrings cpitclaudel/compact-docstrings
git subtree push --prefix=packages/compact-docstrings/
https://github.com/cpitclaudel/compact-docstrings.git master
This seems to have worked nicely. However, I then added an extra commit to the
Github repository, and I'd like to pull it into ELPA. Running
git subtree pull --prefix=packages/compact-docstrings/
github-compact-docstrings master
Gives me the following, which also seems fine:
From github.com:cpitclaudel/compact-docstrings
* branch master -> FETCH_HEAD
Auto-merging packages/compact-docstrings/compact-docstrings.el
Merge made by the 'recursive' strategy.
packages/compact-docstrings/compact-docstrings.el | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
However, when I look at the history that it created, I get three commits
instead of 2: Stefan's change, re-pulled from the GitHub repository; my new
change; and a merge commit.
Is that expected? If not, how can I not re-merge Stefan's change?
Thanks!
Clément.